1. Field of the Invention
The instant invention generally relates to water-resistant corrugated paperboard and a method of preparing the same. More specifically, the instant invention relates to a method of preparing water-resistant corrugated paperboard from sheets that are pre-treated for water-resistance prior to adhering the sheets to form the corrugated paperboard.
2. Background of the Related Art
Water-resistant corrugated paperboard is manufactured and used for shipping produce, wet iced poultry, meat boxes, and a variety of other end uses where the board is exposed to water or high humidity. Conventional water-resistant corrugated paperboard is generally prepared by first assembling the various layers of the corrugated paperboard in a corrugator using specially-formulated adhesives that have higher resistance to water than conventional paperboard adhesives.
Water-resistant paperboard adhesive is prepared through a variety of techniques that generally focus on a higher rate of carrier application and higher solids content. Stein-Hall adhesives are generally used for the water-resistant paperboard adhesive. As known in the art, a Stein-Hall adhesive uses a small portion of cooked carrier starch to suspend and carry uncooked starch. The Stein-Hall adhesive also uses caustic soda (sodium hydroxide) to help cook the carrier starch, and borax to increase tack and cohesiveness. These three raw materials, and water, are the main ingredients for all corrugating adhesives. Their consistency will affect the quality, stability, and running qualities of the finished adhesive.
In order to impart water-resistant properties to the corrugated paperboard, it is know to add a conventional water-proofing resin to the Stein-Hall adhesive. A wide variety of such water-proofing resins are known in the art including recorcinol formaldehyde resins, urea formaldehyde resins and ketone aldehyde resins, e.g., acetone formaldehyde resins.
In one known process, the resulting corrugated paperboard is treated with wax to impart water-resistant properties thereto. In another embodiment, outer surfaces of the liners (i.e., surfaces of the liners that are not adhered to the corrugated medium) are treated with a water-proofing agent prior to assembling the various layers of the corrugated paperboard in the corrugator. However, inner surfaces of the liners and the have not been treated with water-proofing agents in the past due to difficulties associated with adequately adhering the liners to the corrugated medium that is treated with the water-resistant coatings. Further, other considerations have also hindered the development of methodologies for adhering liners to corrugated medium with the inner surfaces of the liners and the corrugated medium treated with the water-proofing agent. Such further considerations include preservation of sufficient Cobb ratings of the resulting corrugated paperboard and prevention of stack lamination when the resulting corrugated paperboards are stacked upon each other after production. Stack lamination is a risk due to the fact that excessively high temperatures of the corrugated paperboard could cause melting and bonding of the stacked corrugated paperboards due to the treatment of the liners with the water-proofing agent, thereby adhering the separate corrugated paperboard in the stack and rendering separation of the corrugated paperboard impossible.
In view of the foregoing, there remains an opportunity to develop a method of preparing water-resistant corrugated paperboard that overcomes the barriers that previously prevented assembly of liners and corrugated medium with the inner surfaces of the liners and the corrugated medium treated with the water-proofing agent.